Pairs of embryonic aortic arches exist during early fetal development and subsequently give rise to the carotid arteries (third arches), the aortic arch (left fourth arch), and the pulmonary arteries and ductus arteriosus (sixth arches). The other aortic arches regress, although the first aortic arches also become part of the maxillary arteries. Congenital defects may arise if development or dissolution of the aortic arches is disrupted. Multiple vascular ring anomalies have been reported in dogs, including persistent right aortic arch, double aortic arch, left aortic arch with right ligamentum arteriosum, and retroesophageal subclavian arteries.
